Water mist systems attack a fire with very fine droplets rather than with a spray. The small droplet size turns the same volume of water into a far larger surface area, so it absorbs heat much faster and displaces some oxygen as it flashes to steam. The practical consequence is far less water, which is why they appear where water damage or tank space is the constraint.
How it works
Nozzles produce droplets small enough that they evaporate in the fire plume rather than falling through it. Evaporation absorbs a great deal of heat and the resulting steam displaces air at the seat of the fire, so the system cools and smothers at once. Because the mechanism depends on droplet size, nozzle design and operating pressure are not details: they are the system.
Where it is used
Heritage buildings where a sprinkler discharge would do more damage than the fire. Residential conversions where a sprinkler tank and pipe sizes cannot be accommodated. Kitchens and cooking lines. Machinery spaces and engine rooms. Data and plant rooms in some designs. In each case the argument is less water, smaller pipework and less tank, rather than better performance in the abstract.
It is not a sprinkler system
Sprinkler systems are designed to a long established set of rules with well understood hazard classifications. Water mist systems are type approved against specific fire test protocols for specific applications, so a system approved for a machinery space is not thereby suitable for a residential corridor. The approval and the application have to match, and that is a question to ask at design stage rather than after installation.
Maintenance
High pressure pumps, fine nozzles and clean water are the three things these systems depend on, and all three degrade. Nozzle apertures are small enough that water quality matters, filters need attention, and the pump set needs the same regime as any other fire pump. A mist system is a lower water system, not a lower maintenance one, and buying it on the former while forgetting the latter is a common mistake.
Questions people ask about fire mist system
Is water mist better than sprinklers?
It is different. Mist uses far less water and smaller pipework, which suits heritage buildings and retrofits. Sprinklers have a long established design framework. The right choice depends on the building and the approved application.
Where are water mist systems used?
Heritage buildings, residential retrofits where a sprinkler tank cannot be accommodated, commercial kitchens, machinery spaces and some plant rooms.
Do mist systems need much maintenance?
Yes. Fine nozzles, high pressure pumps and water quality all matter, so filters, pumps and nozzles need a proper regime. Less water does not mean less servicing.
Where do commercial sprinkler systems fit beside mist?
Sprinklers are the ordinary whole building answer and the one most design guidance is written around. Mist is chosen where the water volume a sprinkler needs is the problem: a listed interior, a building with no room for the tanks, or a space where the water damage would be worse than the fire.
When is a commercial fire sprinkler system the better choice?
Where the building has the water supply and the space for it, and where covering the whole premises matters more than limiting the volume discharged. Sprinklers have the deepest design guidance behind them, which makes approval and insurance straightforward in a way mist still is not.
Where does a residential sprinkler system fit?
In dwellings and residential blocks, at a much lower flow than a commercial scheme because it is protecting a single room of origin rather than a warehouse. That is why it can often run from the mains where a commercial design would need a tank.